This invention relates to a method and apparatus for unloading x-ray film cassettes and more particularly to a method and apparatus using an air stream to assist in unloading x-ray film from cassettes that have a load/unload slot in one edge.
In the development of x-ray film handling systems, equipment has been provided which allows the automatic loading (and unloading) of x-ray film into a cassette under daylight conditions. Such equipment frees the operator from the need to load and unload the film to and from a cassette in a darkroom. Exemplary of such automatic system is that disclosed in U.S. Reissue No. 30,792 (Schmidt) assigned to the assignee of the instant invention. This reissue patent describes an x-ray film package for use with a daylight side loading cassette of the type disclosed in U.S. Pat. Nos. 3,784,835 and 3,870,889 (both issued to Schmidt and both assigned to the assignee of the present application). U.S. Pat. No. 3,715,087 (Schmidt) describes a device used for unloading cassettes of the type disclosed in the last mentioned patents under daylight conditions.
In operation, the x-ray film sheet is automatically side loaded through a side slot into the cassette which is operative to hold the film between two opposed substantially parallel x-ray intensifying screens during the period of patient exposure. Following exposure, the screens are separated thereby unclamping the film sheet. The cassette is unloaded under the influence of gravity by allowing the film sheet to slip out of the cassette through the side slot. This is accomplished by a device as disclosed in the last mentioned patent which is adapted to release one of the two cassette plates holding the intensifying screens to thereby release the holding pressure from the film sheet and allow it to drop under the influence of gravity into a lighttight container.
For a variety of reasons it is important that the time required for the film to drop from the cassette be maintained to within a reasonable maximum on the order of approximately seven seconds. It is believed to be most advantageous if the film drop time occupy on the order of two to three seconds. However, it has been found that in cassettes embodying the teachings of the above referenced patents, the x-ray film often develops a tendency to adhere to one or the other of the intensifying screens even after the holding pressure is relieved therefrom. Attempts have been made to overcome this problem through the use of cautilevered conical actuators disposed along the cassette edges which are actuated by an actuating cam assembly and pivot inwardly of the cassette to thereby edgewise engage the film sheet and buckle the same to create a gap between the sheet and the screen. Air leakage into the gap tends to equalize the pressure forces on both sides of the sheet to permit it to respond to the influence of gravity and drop from the cassette.
U.S. Pat. No. 4,383,330 (DeFelice, et al.), assigned to the assignee of the present invention, discloses an improvement in the conical bucklers used in the prior art. However, the employment of bucklers to release the film requires cassettes especially designed to accommodate them. It is believed to be advantageous to provide an apparatus and a method which can accept an x-ray cassette of the type disclosed in U.S. Pat. Nos. 3,784,835 and 3,870,889, or other similar cassettes and which do not require special modifications for the quick release of the film therefrom.